Circuit Description
The transmission internal mode switch (IMS) is a sliding contact switch attached to the lower control valve body, within the transmission. The manual valve link assembly then connects the IMS to the manual valve. The 4 inputs to the transmission control module (TCM) from the IMS indicate which position is selected by the transmission selector lever. This information is used for engine controls as well as determining the transmission shift patterns. The input voltage level at the TCM is high, ignition voltage, when the IMS is open and low when the switch is closed to ground. The state of each input is available for display on the scan tool. The four input parameters represented are Signal A, Signal B, Signal C and Signal P, Parity.
If the TCM detects a combination of IMS inputs that are invalid, then DTC P1825 sets. DTC P1825 is a type B DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P1825 Internal Mode Switch - Invalid Range
Conditions for Running the DTC
The engine run time is greater than 5 seconds.
Conditions for Setting the DTC
The TCM detects an invalid IMS range for 8 seconds.
Action Taken When the DTC Sets
| • | The TCM requests the engine control module (ECM) to illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met. |
| • | The TCM commands maximum line pressure. |
| • | The TCM freezes transmission adaptive functions. |
| • | The ECM records the operating conditions when the Conditions for Setting the DTC are met. The ECM stores this information as Freeze Frame and Failure Records and the TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as Failure Records. |
| • | The TCM stores DTC P1825 in TCM history during the second consecutive trip in which the Conditions for Setting the DTC are met. |
Conditions for Clearing the MIL/DTC
| • | The ECM turns OFF the MIL after the third consecutive drive trip in which the TCM does not send a MIL illumination request. |
| • | The TCM clears the DIC message when the condition no longer exists. |
| • | A scan tool can clear the MIL/DTC. |
| • | The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring. |
| • | The TCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the TCM. |
Diagnostic Aids
Refer to Transmission Internal Mode Switch Logic .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests the IMS for an open ground circuit.
-
This step tests for correct reference voltage from the TCM.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 |
Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the TCM. Does each range selected match the scan tool IMS display? | -- | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 |
Does the IMS A/B/C/P display match the specified value for each range selected? | HI/HI/HI/HI | Go to Step 13 | Go to Step 4 | |
4 |
Does the scan tool IMS A/B/C/P parameter indicate HI for all range signal states? | -- | Go to Step 5 | Go to Step 9 |
Refer to Automatic Transmission Inline 20-Way Connector End View . Does the voltage measure ignition voltage at all four terminals? | -- | Go to Step 6 | Go to Step 10 | |
6 | Connect a fused jumper wire from terminal F of the J 44152 , signal A circuit, to ground while monitoring the scan tool IMS A/B/C/P parameter. Refer to Automatic Transmission Inline 20-Way Connector End View . When the signal A circuit is grounded, do any other signal circuits indicate LOW? | -- | Go to Step 11 | Go to Step 7 |
7 | Connect a fused jumper wire from terminal G of the J 44152 , signal B circuit, to ground while monitoring the scan tool IMS A/B/C/P parameter. Refer to Automatic Transmission Inline 20-Way Connector End View . When the signal B circuit is grounded, do any other signal circuits indicate LOW? | -- | Go to Step 11 | Go to Step 8 |
8 | Connect a fused jumper wire from terminal H of the J 44152 , signal C circuit, to ground while monitoring the scan tool IMS A/B/C/P parameter. Refer to Automatic Transmission Inline 20-Way Connector End View . When the signal C circuit is grounded, do any other signal circuits indicate LOW? | -- | Go to Step 11 | Go to Step 12 |
9 | Test the signal circuits of the IMS that did not indicate HI for a short to ground between the TCM connector and the AT inline 20-way connector. Refer to Testing for Short to Ground and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 17 |
10 | Test the signal circuits of the IMS that did not indicate ignition voltage for an open between the TCM connector and the AT inline 20-way connector. Refer to Testing for Continuity and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 17 |
11 | Test the affected signal circuits of the IMS for a shorted together condition between the TCM connector and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 17 |
12 | Test the signal circuits of the IMS for an open or shorted condition between the AT inline 20-way connector and the IMS. Refer to Circuit Testing . Did you find a condition? | -- | Go to Step 15 | Go to Step 16 |
13 | Test the ground circuit of the IMS for an open between the AT inline 20-way connector and the ground distribution block. Refer to Testing for Continuity and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 14 |
14 | Test the ground circuit of the IMS for an open between the AT inline 20-way connector and the IMS. Refer to Testing for Continuity . Did you find a condition? | -- | Go to Step 15 | Go to Step 16 |
15 |
Important: The automatic transmission wiring harness consists of 2 separate harnesses, the Automatic Transmission Wiring Harness Assembly and the Automatic Transmission Wiring Extension Harness Assembly. In order to avoid the unnecessary replacement of parts, determine which harness contains the fault and replace only that harness. Replace the automatic transmission wiring harness. Refer to Input Speed Sensor and Wiring Harness Removal in the 4T80-E section of the Transmission Unit Repair Manual. Did you complete the replacement? | -- | Go to Step 18 | -- |
16 | Replace the transmission internal mode switch. Refer to Control Valve Lower Body Disassemble in the 4T80-E section of the Transmission Unit Repair Manual. Did you complete the replacement? | -- | Go to Step 18 | -- |
17 | Replace the TCM. Refer to Control Module References . Did you complete the replacement? | -- | Go to Step 18 | -- |
18 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | Go to Step 19 | Go to Step 2 |
19 | With the scan tool, observe the stored information, capture info. and DTC info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK |
